1. Field of the Invention
The present invention relates to a magnetic recording medium for use in magnetic recording devices. The invention further relates to a method for manufacturing and a device employing a magnetic recording medium according to the present invention.
2. Description of the Related Art
Various compositions and structures have been proposed for magnetic layers and non-magnetic under-layers in high-recording-density and low-noise magnetic recording mediums. In particular, a magnetic layer called a granular magnetic layer, has been proposed having a structure in which ferromagnetic grain are surrounded by a non-magnetic non-metallic substance.
Japanese Unexamined Patent Application Publication No. 08-255342, discloses attaining low noise by forming a granular recording layer in which ferromagnetic grains are dispersed in a non-magnetic film, by a method including steps of sequentially depositing a non-magnetic film, a ferromagnetic film and a non-magnetic film on a non-magnetic substrate, and heat treating the laminate. In this specific non-magnetic film, oxides or nitrides of silicon are used.
U.S. Pat. No. 5,679,473 discloses a granular recording film in which each magnetic grain is surrounded and separated by a non-magnetic oxide by means of RF sputtering using a CoNiPt target including an oxide, such as SiO2. A granular recording film with high coercive force and low noise is achieved by this patent. Further, since the granular magnetic layer facilitates separation of magnetic grains even by lamination without heating, an inexpensive non-magnetic substrate such as injection-molded plastic maybe used. Consequently, the granular magnetic layer provides partial cost reduction during manufacture.
An alloy with hexagonal closest packed (hcp) lattice structure composed mainly of cobalt is commonly used for magnetic layers in magnetic recording medium. It is necessary to orient the C-axis of the hcp structure to the film surface in order to obtain excellent characteristics. This orientation is accomplished in a conventional magnetic recording medium by controlling crystal orientation of an under-layer and making the magnetic layer epitaxially grow on such an under-layer. Unfortunately, in a magnetic recording mediums having a granular magnetic layer, controlling crystal orientation of the magnetic layer has been considered to be difficult because the epitaxial growth is hindered by the existence of oxides or nitrides.
Recently, it has been shown that crystal orientation control of the magnetic layer is still possible, in magnetic recording mediums having granular magnetic layers, by controlling the structure of the under-layer.
A report from the abstract of the 22nd Conference of the Magnetics Society of Japan, P. 469 (1998), entitled xe2x80x9cEffect of Crxe2x80x94Mo under-layer in a CoPtxe2x80x94SiO2 mediumxe2x80x9d discloses that low noise was attained by provision of an under-layer of CrMo alloy for the granular magnetic layer and controlling the lattice constants of the under-layer with varied amount of molybdenum. Another document from the abstract of the 24th Conference of the Magnetics Society of Japan, p.21 (2000), entitled xe2x80x9cA high coercive force medium that need not heating in lamination processxe2x80x9d discloses that low noise was also attained by forming a ruthenium layer beneath the granular layer.
Unfortunately, while information in the processing field shows rapid development in recent years, this development demands much more extensive improvement over presently achieved levels for noise reduction.
It is an object of the present invention to provide a magnetic recording medium, a method for manufacturing a magnetic recording medium, and a magnetic recording device which overcome the drawbacks of the related art noted above.
It is another object of the present invention to achieve further noise reduction in a magnetic recording medium by more precise control of structure of magnetic grains.
It is another object of the present invention to provide a magnetic recording medium achieving more reduction of noise by forming a plurality of intermediate layers on an under-layer before laminating the magnetic layer.
It is another object of the present invention to provide a method for manufacturing such a medium and to provide a magnetic recording device comprising such a medium.
It is another object of the present invention to provide a magnetic recording medium and a method of manufacturing the same which provides manufacturing cost savings while maintaining or increasing recording quality.
The present invention relates to a magnetic recording medium, method of manufacturing a magnetic recording medium and magnetic recording devices wherein a plurality of non-magnetic metallic intermediate layers is laminated between an under-layer and a magnetic layer. One of the intermediate layers is composed of at least an element selected from the group consisting of Ru, Re and Os and contains oxygen, and another is composed of a CoCr alloy containing at least an element selected from the group consisting of Nb, Mo, Ru, Rh, Pd, Ta, W, Re Os, Ir and Pt. The resulting magnetic recording medium provides reduced costs and improved recording characteristics.
According to an embodiment of the present invention there is provided, a magnetic recording medium comprising: a non-magnetic substrate, at least a non-magnetic under-layer on the non-magnetic substrate, at least a first non-magnetic metallic intermediate layer on the non-magnetic under-layer, at least a second non-magnetic metallic intermediate layer on the first non-magnetic metallic intermediate layer, at least a magnetic layer on the second non-magnetic metallic intermediate layer, at least a protective film and a liquid lubricant layer sequentially laminated on the magnetic layer, the magnetic layer being a plurality of ferromagnetic grains and non-magnetic grain boundaries, the plurality of ferromagnetic grains containing at least cobalt and platinum, the non-magnetic grain boundaries including at least an oxide substantially surrounding the plurality of ferromagnetic grains, the first intermediate layer containing oxygen and being composed of at least one element selected from the group consisting of Ru, Re and Os, and the second intermediate layer being at least a CoCr alloy including at least one element selected from the group consisting of Nb, Mo, Ru, Rh, Pd, Ta, W, Re, Os, Ir and Pt.
According to another embodiment of the present invention there is provided, a magnetic recording medium, wherein: the non-magnetic substrate is at least a first plastic, the first plastic being at least one of a polycarbonate and a polyolefin.
According to another embodiment of the present invention there is provided, a magnetic recording medium, wherein: a crystal structure of the second intermediate layer is hexagonal close packed, a crystal structure of the plurality of ferromagnetic grains in the magnetic layer is hexagonal close packed, and a misfit between lattice constants of unit cells of the second intermediate layer and unit cells of the plurality of ferromagnetic grains is within xc2x13%.
According to another embodiment of the present invention there is provided, a magnetic recording medium, wherein: the under-layer is at least one of chromium and a chromium alloy, and at least one of a (200) lattice plane and a (211) lattice plane in the under-layer is preferentially oriented in parallel with a film surface of the under-layer.
According to another embodiment of the present invention there is provided, a method for manufacturing a magnetic recording medium comprising the steps of: laminating at least a non-magnetic under-layer on a non-magnetic substrate, laminating at least a first non-magnetic metallic intermediate layer on the non-magnetic under-layer, laminating at least a second non-magnetic metallic intermediate layer on the first non-magnetic metallic intermediate layer, laminating at least a magnetic layer on the second non-magnetic metallic intermediate layer, laminating a protective film on the magnetic layer, laminating a liquid lubricant layer on the protective film, the step of laminating the magnetic layer including laminating to form at least ferromagnetic grains and non-magnetic grain boundaries surrounding the grains, the grains being at least one of cobalt and platinum and the grain boundaries being at least an oxide, the step of laminating the first intermediate layer including laminating to form the first intermediate layer from oxygen and at least one element selected from the group consisting of Ru, Re, and Os, and the step of laminating the second intermediate layer including laminating to form the second intermediate layer from a CoCr alloy containing at least one element selected from the group consisting of Nb, Mo, Ru, Rh, Pd, Ta, W, Re, Os, Ir and Pt.
According to another embodiment of the present invention there is provided, a method for manufacturing a magnetic recording medium, wherein: the non-magnetic substrate is at least a first plastic, and the first plastic being at least one of a polycarbonate and a polyolefin.
According to another embodiment of the present invention there is provided, a method for manufacturing a magnetic recording medium, wherein: the step of laminating the second intermediate layer including laminating to form a crystal structure of the second intermediate layer as hexagonal close packed, the step of laminating the magnetic layer including laminating to form a crystal structure of the ferromagnetic grains in the magnetic layer as hexagonal close packed, and the steps of laminating the second intermediate layer and the magnetic layer including laminating to form a misfit between lattice constants of unit cells of the second intermediate layer and unit cells of the ferromagnetic grains of within xc2x13%.
According to another embodiment of the present invention there is provided, a method for manufacturing a magnetic recording medium, wherein: the step of laminating the under-layer including laminating to form the under-layer from at least one of chromium and a chromium alloy, and the step of laminating the under-layer including laminating to form at least one of a (200) lattice plane and a (211) lattice plane in the under-layer as preferentially oriented in parallel with a film surface of the under-layer.
According to another embodiment of the present invention there is provided, a magnetic recording device comprising: a magnetic recording medium as defined above.
According to another embodiment of the present invention, there is provided, a magnetic recording medium comprising: a non-magnetic substrate, at least a non-magnetic under-layer on the non-magnetic substrate, at least a first non-magnetic metallic intermediate layer on the non-magnetic under-layer, at least a second non-magnetic metallic intermediate layer on the first non-magnetic metallic intermediate layer, at least a magnetic layer on the second non-magnetic metallic intermediate layer, at least a protective film and a liquid lubricant layer sequentially laminated on the magnetic layer, the magnetic layer being a plurality of ferromagnetic grains and non-magnetic grain boundaries, the plurality of ferromagnetic grains containing at least cobalt and platinum, the non-magnetic grain boundaries including at least an oxide substantially surrounding the plurality of ferromagnetic grains, the first intermediate layer being at least a CoCr alloy including at least one element selected from the group consisting of Nb, Mo, Ru, Rh, Pd, Ta, W, Re, Os, Ir and Pt, and the second intermediate layer containing oxygen and being composed of at least one element selected from the group consisting of Ru, Re and Os.
According to another embodiment of the present invention, there is provided, a magnetic recording medium, wherein: the non-magnetic substrate is at least a first plastic, the first plastic being at least one of a polycarbonate or polyolefin.
According to another embodiment of the present invention, there is provided, a magnetic recording medium, wherein: a crystal structure of the first intermediate layer is hexagonal close packed, a crystal structure of the second intermediate layer is hexagonal close packed, and a misfit between lattice constants of unit cells of the first intermediate layer and unit cells of the second intermediate layer is within xc2x13%.
According to another embodiment of the present invention, there is provided, a magnetic recording medium, wherein: the under-layer is at least one of chromium and a chromium alloy, and at least one of a (200) lattice plane and a (211) lattice plane in the under layer is preferentially oriented in parallel with a film surface of the under-layer.
According to another embodiment of the present invention, there is provided, a method for manufacturing a magnetic recording medium comprising the steps of: laminating at least a non-magnetic under-layer on a non-magnetic substrate, laminating at least a first non-magnetic metallic intermediate layer on the non-magnetic under-layer, laminating at least a second non-magnetic metallic intermediate layer on the first non-magnetic metallic intermediate layer, laminating at least a magnetic layer on the second non-magnetic metallic intermediate layer, laminating a protective film on the magnetic layer, laminating a liquid lubricant layer on the protective film, the step of laminating the magnetic layer including laminating to form at least ferromagnetic grains and non-magnetic grain boundaries surrounding the grains, the grains being at least one of cobalt and platinum and the grain boundaries being at least an oxide, the step of laminating the first intermediate layer including laminating to form the first intermediate layer from a CoCr alloy containing at least one element selected from the group consisting of Nb, Mo, Ru, Rh, Pd, Ta, W, Re, Os, Ir and Pt, and the step of laminating the second intermediate layer including laminating to form the second intermediate layer from oxygen and at least one element selected from the group consisting of Ru, Re, and Os.
According to another embodiment of the present invention, there is provided, a method for manufacturing a magnetic recording medium, wherein: the non-magnetic substrate is at least a first plastic, and the first plastic is at least one of a polycarbonate and a polyolefin.
According to another embodiment of the present invention, there is provided, a method for manufacturing a magnetic recording medium, wherein: the step of laminating the first intermediate layer including laminating to firm a crystal structure of the first intermediate layer as hexagonal close packed, the step of laminating the second intermediate layer including laminating to form a crystal structure of the second intermediate layer as hexagonal close packed, and a misfit between lattice constants of unit cells of the first intermediate layer and unit cells of the second intermediate layer is within xc2x13%.
According to another embodiment of the present invention, there is provided, a method for manufacturing a magnetic recording medium, wherein: the step of laminating the under-layer including laminating to form the under-layer from at least one of chromium and a chromium alloy, and the step of laminating the under-layer including laminating to form at least one of a (200) lattice plane and a (211) lattice plane in the under-layer as preferentially oriented in parallel with a film surface of the under-layer.
According to another embodiment of the present invention there is provided, a magnetic recording device comprising: a magnetic recording medium as defined by the above eight paragraphs.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.